Differential Wheel Braking Control for U-Split EV Deceleration
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Solution Overview
Problem
Existing slip control systems in electrically powered motor vehicles face challenges in coordinating the actuators of the drive apparatus and wheel braking apparatuses, particularly in situations with inhomogeneous friction values between wheels, leading to suboptimal deceleration and handling.
Innovation Solution
A control structure that activates the drive apparatus according to a torque target value and wheel braking apparatuses based on differential speed, ensuring optimal speed control by integrating separate torque and speed limit values, and using a central control apparatus to coordinate actuators, thereby avoiding excessive yaw torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the drive apparatus is activated according to torque target value alone, then the deceleration control is simplified, but the wheel speed control precision deteriorates in u-split situations
Solution Approach 1:
The control system is segmented into two independent control loops: one controlling axle speed via the drive apparatus based on torque target values, and another controlling wheel speed differential via wheel braking apparatus. This segmentation allows each loop to focus on specific control aspects, improving overall precision without excessive complexity.
Solution Approach 2:
The control system introduces an intermediary mechanism that coordinates between the drive apparatus and wheel braking apparatus. The central control device acts as an intermediary, distributing control tasks appropriately - using the drive apparatus for primary deceleration and wheel braking apparatus for differential speed correction, thereby achieving precise control through coordinated action.
2Measurement precision
If wheel braking apparatuses are activated based on differential speed, then the wheel speed control precision is improved, but the device complexity increases
Solution Approach 1:
The wheel braking apparatus serves multiple functions: it provides primary braking when needed and acts as a differential speed regulator when activated based on differential speed. This multi-functionality allows the system to achieve precise wheel speed control without adding dedicated differential braking mechanisms, thereby managing complexity.
Solution Approach 2:
The control system dynamically adjusts the activation strategy based on operating conditions. In homogeneous friction conditions, only the drive apparatus is activated. In u-split situations, the wheel braking apparatus is dynamically engaged to provide additional differential correction, optimizing precision while minimizing unnecessary complexity in normal conditions.
3Force
If three actuators act on two wheels via differential gear, then the braking torque is increased, but the coordination difficulty increases
Solution Approach 1:
The control system applies local quality by assigning different control roles to different actuators based on local conditions. The drive apparatus (first actuator) handles the majority of braking torque generation through torque target control, while the wheel braking apparatus (second and third actuators) provides localized differential correction based on individual wheel speed measurements, optimizing the force distribution.
Solution Approach 2:
The system uses partial action by not always activating all three actuators simultaneously. In homogeneous friction conditions, only the drive apparatus is activated. The wheel braking apparatus is activated partially or excessively only when differential speed exceeds thresholds, providing additional braking torque precisely when needed without the continuous coordination complexity of managing all three actuators always active.
Data Source
AI summary
A method for operating a motor vehicle. The motor vehicle has an axle having a first and a second wheel coupled to one another by a differential gear. The wheels are also assigned a drive apparatus having an activatable first actuator via the differential gear. The first wheel, assigned to a left side of the motor vehicle, is assigned a first wheel braking apparatus having an activatable second actuator, and the second wheel, assigned to a right side, is assigned a second wheel braking apparatus having an activatable third actuator. A torque target value is specified according to a braking request, the first actuator is activated at least according to the torque target value for fulfilling the braking request, and the second and the third actuators are activated according to a difference between an actual speed of the first wheel and an actual speed of the second wheel.